JACKSON, Mississippi — The Mississippi Supreme Court ruled Thursday that circuit clerks must redact voters’ birthdates before poll books are open for public inspection.

The ruling is a blow to state Sen. Chris McDaniel’s effort to examine election materials as he seeks evidence of improper voting to challenge his loss to six-term U.S. Sen. Thad Cochran in the June 24 Republican primary runoff.

McDaniel’s attorneys said they need to see dates of birth and other identifying information so they can tell the difference between voters with similar names.

Certified results show Cochran won by 7,667 votes, but McDaniel has not conceded more than three weeks after the election.

Justices ruled that poll books are controlled by the state Public Records Act, which specifies that Social Security numbers, telephone numbers, dates of birth and age information must be redacted before the public can examine certain documents.

McDaniel’s attorneys said Wednesday that the tea party-backed state senator from Ellisville could file a challenge of his loss to Cochran within about the next 10 days. His first challenge would be filed with the state Republican executive committee. Then, after about another 10 days, he could file a lawsuit asking a state court judge to order a new election.

McDaniel has released no documents to substantiate his claims that thousands of voting irregularities occurred June 24.

The only registered voters prohibited from casting a ballot in the June 24 Republican runoff were those who had voted in the June 3 Democratic primary. Mississippi voters do not register by party, but state law bans people from voting in one party’s primary and another party’s runoff in the same cycle.

Cochran strategist Austin Barbour said Wednesday that the incumbent’s campaign is turning his attention to the general election. The Nov. 4 ballot will also include Democratic former U.S. Rep. Travis Childers and the Reform Party’s Shawn O’Hara.